Support is requested for a Keystone Symposia meeting entitled B Cell Development and Function, organized by Max D. Cooper, Andrea Cerutti and Carola G. Vinuesa. The meeting will be held in Keystone, Colorado from February 10 - 15, 2013. This meeting will provide an overview of the most recent advances in the biology of B cells. In addition to covering the function of B cells under steady-state conditions and infection, the meeting will provide an update on the alterations of B cells in autoimmunity, leukemia, and lymphoma. The mechanisms by which B cells crosstalk with different components of the innate and adaptive immune systems and the contribution of distinct B cell subsets to systemic and mucosal immunity remain unclear, particularly in humans. This meeting has the following specific aims: 1) to define the factors involved in B cell lineage specification and reprogramming; 2) to elucidate the evolution and mechanisms of the processes underpinning antibody gene diversification; 3) to better understand the B cell pathways required for systemic and mucosal antibody responses against T cell-dependent and T cell-independent antigens; 4) to clarify the mechanisms by which antibodies provide protection against HIV; 5) to broaden our understanding of the molecular alterations associated with autoimmune and neoplastic B cell disorders; and 6) to provide an interactive forum to involve early stage investigators and highlight their discoveries. By addressing these problems, this meeting will not only generate new knowledge on the biology of B cells in health and disease states, but it will also provide a framework for investigators and clinicians to generate new ideas, initiate new collaborations, and eventually introduce changes in clinical practice. In addition, this meeting will provide a unique opportunity to take a closer look at B cells by linking experts in B cell biology with experts in stem cell biology, comparative immunology, molecular biology, and in vivo imaging. Additional opportunities for interdisciplinary interactions will be significantly enhanced by the concurrent meeting on HIV Vaccines, which will share a keynote session and two plenary sessions with this meeting.